I don't mean they have to specifically have this or that account, the point is building your own portfolio of work and a history of productive professional engagement has never been easier. Maybe you already have a work history that puts you beyond that kind of issue, but for those who don't there are numerous ways to build a presence. Don't like GitHub or programming phones? Heroku has a free tier and there's always Google AppEngine. SO doesn't float your boat? How about a blog on a subject that does? I can't even count the ways a young techie has to stand out from the crowd. I'm not saying it's required or in any way mandatory from my perspective, but given a choice between two otherwise similar candidates, the one with an engaging and accessible portfolio of work will win out.
Most of the software that gainfully employed engineers work on all day is owned by the company they work for (or consult for). If you disclose any details about it, you may be sued [google "Sergey Aleynikov" :-)]
Yes indeed. But I completely fail to see how that is relevant to my point. Im not saying anything about posting code that belongs to other people, even if you wrote it, and I'm mainly talking about those without a commercial track record. Although even then, having some spare time projects on GitHub never seems to have hurt my prospects in interviews.
I'd like to think I'm not that uncommon for a geek. I love coding. (I have been coding since the 80s, and professionally since the late 90s. You will find my name in a handful of credits files, and a number of mailing list and usenet posts.)
But I won't start using centralized services just because you or some recruiter decides it's the new cool place to be. Sorry.